Respiratory physiology Flashcards
The purpose of the pulmonary system is to:
supply oxygen from the atmosphere to the blood while removing CO2 help maintain acid-base balance allow for phonation provide for pulmonary defense provide oxygen for metabolism
Partial pressure of gases in the air include:
nitrogen: 78%
oxygen: 21%
CO2 and trace gases: 1%
Glycolysis makes
2 ATP, has no mitochondria involvement–> pyruvate and lactic acid result
Pyruvate and acetyl CoA combine to form
2 more ATP and CO2 production
Aerobic metabolism produces
34 ATP via the electron transport
utilizes O2
byproducts include: CO2, H20, and heat
The larynx consists of
9 cartilages
3 paired- corniculate, cuneiform, arytenoid
3 unpaired- epiglottis, thyroid, and cricoid
The nose is used for
filtration, smell, and humidification of incoming air
The airways consists of the
nose, mouth, pharynx, larynx, trachea, and lower airways
Sensory innervation to the larynx is via the
internal superior laryngeal nerve- vocal cords and above
recurrent laryngeal nerve- below the vocal cords
Motor innervation in the larynx is via the
recurrent laryngeal nerve to all but the cricothyroid muscle which is innervated by external superior laryngeal nerve
Abduction to the vocal cords is via the
posterior cricoarytenoid- please come apart
Adduction of the vocal cords is via the
lateral cricoarytenoid- “let’s close airway”
Tension to the vocal cords is via the
cricothyroid- “cords tense”
laryngospasm
Relaxation to the vocal cords is via the
thryoarytenoid- “they relax”
Describe the difference between the right and left bronchus is
the right main bronchus is shorter, wider, and more vertical (25 degree angle) than the left bronchus which is why a right mainstem intubation is more likely than a left
The left main bronchus has a 45 degree angle off the trachea
Where are the tracheal rings and what is the purpose
the tracheal rings sit anteriorly and prevent tracheal collapse
The role of the trachea and bronchi is to
transport gases between the atmosphere and the lung parenchyma
Describe the TLC in the left and right lungs:
the right lung makes up 55% TLC and is divided into 3 lobes
the left lung makes up 45% TLC and is divided into 2 lobes
The conducting zone is where
no gas exchange exists
goblet and mucous exist here
The transitional and respiratory zones are where
gas exchange occurs
absence of goblet cells
The diaphragm is the
primary muscle of ventilation
Innervation to the diaphragm comes from
C3, C4, and C5 nerve roots bilaterally to form the phrenic nerves
Internal intercostal muscles help with
forced expiration
External intercostals help with
forced inhalation
The lungs are made up of 3 types of pneumocytes:
Type 1- structural
Type 2- surfactant producing
Type 3- Macrophages (alveolar)
The surface area of the alveoli are
60-80 meters^2
The distance from the front incisors to the carina is approximately
26 cm
front incisors to larynx= 13 cm
larynx to carina= 13 cm
The respiratory zone consists of
the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli
gas exchange occurs here
The blood supply for the respiratory zones are from
the pulmonary circulation
Since respiratory bronchioles have a 0.5 mm diameter and smaller, gas flow is
so slow that gas moves more by diffusion rather than by bulk flow
The conducting zone is where
no gas exchange occurs
from the nose/mouth to the terminal bronchioles
The blood supply to the conducting zone is from the
thyroid, bronchial, and internal thoracic arteries (i.e. systemic circulation)
Terminal bronchioles measure
1 mm in diameter and lose cartilaginous plates
______ makes up the anatomic dead space
the conducting zone
Anatomic dead space can be estimated by any of the following:
150 mLs
1/3 the tidal volume
1 mL/lb or 2 mLs/kg of body weight
Describe how the respiratory cycle occurs
nerve impulse is sent to phrenic nerves and travels to the diaphragm
the diaphragm contracts and increases the superior-inferior dimension of the chest
external intercostal muscles help to lift the sternum and elevate the ribs increasing the A-P diameter
expiration is primarily a passive process
elastic forces in the lung, chest wall, and abdomen ehlp to compress the lungs
internal intercostals can help in forceful exhalation
Inspiratory muscles include
sternocleidomastoid, scalene
Expiratory muscles include
rectus, intenral/external obliques, transversus abdominus
The only time you could generate a positive intrathoracic pressure is during
forced expiration
The transpulmonary pressure is the
difference between the intrapleural and intra-alveolar pressures, and it determines the size of the lungs
A higher transpulmonary pressure corresponds to a larger lung
Work of breathing consists of
elastic and resistive work:
must overcome elastic and resistive forces of the lung and chest wall
work done to overcome airway resistance: can be natural or artificial airway devices and circuits
Neuronal control of the lungs is via the
brain stem by the medulla and pons
The medulla consists of the
dorsal respiratory group which stimulates inspiration- “Pacemaker for breathing”
the ventral respiratory group stimulations inspiration/expiration-helps with forced inspiration/expiration
The Pons control is via the
pneumotaxic center- decreases tidal volume for fine control of tidal volume - located high in the pons
the apneustic center- increases tidal volume for long and deep breathing
located lower in the pons
Output for the apneustic center is limited by
baroreflex input from the lung
input from the pneumotaxic center
The humoral control of breathing consists of:
the central and peripheral chemoreceptors that help regulate ventilation
The central chemoreceptors respond to
hydrogen ion levels
The peripheral chemoreceptors respond to
CO2, pH, and hypoxemia
The normal stimulus to breathe is
hypercapnia
Cranial nerve X- the vagus nerve carries the
aortic arch and lung stretch signals to the DRG
Cranial nerve IX- the glossopharyngeal carries the
carotid body signals to the DRG
Tidal volumes should be set to
6-8 mL/kg of IBW
Parasympathetic control of the airway comes from
the vagus nerve
causes mucus secretion, increased vascular permeability, vasodilation, and bronchospasm
bronchoconstriction is greatest in the upper airways
Activation of the M3 receptors results in
bronchoconstriction
Sympathetic control of the airway
has little input on tissues
inhibits mediator release from mast cells
increases mucociliary clearance
Activation of B2 receptors (exogenously) results in
bronchodilation
Lung volumes include
residual volume- cannot be measured with spirometry
expiratory reserve volume
tidal volume
inspiratory reserve volume
The capacities of the lungs include
(made of 2 or more volumes) Inspiratory capacity (IC= IRV +Vt) vital capacity (VC= IRV+Vt+ERV) Functional residual capacity (FRC= RV+ERV) Total lung capacity (TLC= IRV+ Vt+ ERV+RV)
Inspiratory capacity is made up of
inspiratory reserve volume and tidal volume
vital capacity is made up of
inspiratory reserve volume, tidal volume, and expiratory reserve volumes
Functional residual capacity is made up of
residual volume and expiratory reserve volume
Total lung capacity is made up of
inspiratory reserve volume, tidal volume, expiratory reserve volume and residual volume
The respiratory quotient is
0.8
varies based on macronutrient metabolism
FRC represents the point where
elastic recoil force of the lung is in equilibrium with the elastic recoil of the chest wall
FRC represents the
“oxygen reserve”
Factors that affect FRC include
upright and prone position increase FRC
supine decreases FRC
muscle relaxation decreases FRC
Describe the pleuras in the lung
The lung is covered by the visceral pleura while the chest wall is covered by the parietal pleura
The space between the visceral pleura and the parietal pleura is known as the
pleural cavity
A small amount of serous fluid is maintained in this space to reduce friction
When air occupies the pleural cavity it is known as
the pneumothorax
Air under pressure in the pleural cavity is known as
tension pneumothorax
Blood in the pleural cavity is known as
hemothorax
Excess serous fluid in the pleural cavity is known as
pleural effusion
Empyema or pyothorax is
pus in the pleural cavity
An organized blood clot in the pleural cavity is known as
fibrothorax
Lymph in the parietal pleura is known as
chylothorax
Compliance is a change in
volume divided by a change in pressure
Static compliance is the compliance of
the lung and chest wall with NO AIR Movement
airway resistance doesn’t play a role in this calculation
Reasons for decreased static compliance include
fibrosis, obesity, edema, vascular engorgement, ARDs, external compression, and atelectasis
Static compliance can be calculated via
Cst= tidal volume/ (plateau pressure-PEEP)
normal value is 60-100 mL/ cmH2O
To measure a plateau pressure, you have to set an
inspiratory pause on the ventilator. Most vents can only do this in volume control ventilation
Dynamic compliance is the
compliance of lung and chest wall during a breath
airway resistance plays a large role in this calculation
Reasons for decreased dynamic compliance include:
bronchospasm, tube kinking, mucous plugs, increased RR
anything that increases airway resistance!
Dynamic compliance is calculated by
Cdyn= tidal volume/ (peak pressure- PEEP)
Normal value is 50-100 mL/cmH20
What plays the largest role in reducing surface tension?
surfactant
it helps prevent atelectasis and small airway collapse
Elastic forces are greatest in
collapsed and hyperinflated alveoli
this means they require a greater change in pressure to achieve a set increase in volume
Laminar flow through the lungs is found mostly in
small airways
Turbulent flow through the lungs is found mostly in
large airways
The greatest airway resistance is in the
medium sized bronchi
Reynolds number is used
to predict when flow will be laminar or turbulent
A reynolds number of 2000 or below is indicative of
laminar flow
A Reynold’s number of 4000 and above is indicative of
turbulent flow
A Reynold’s number between 2000-4000 is considered
transitional flow
Poiseuille’s law is used to determine
resistance to flow
radius is the most important factor in resistance to flow
The West zones are
zones comparing alveolar pressure, arterial pressure, and venous pressure
Zone 1 is where
Alveolar>arterial> venous pressure
V/Q= >1
Zone 2 is where
Arterial>alveolar>venous pressure
V/Q=1
Zone 3 is where
arterial>venous pressure>alveolar
V/Q= 0.8
Zone where the PA catheter tip should be placed
alveoli have the greatest compliance and perfusion
Zone 4 is where
arterial>interstitial>venous pressure>alveolar V/Q <1
Zone 4 is a disease state
The closing volume is the
volume above residual volume where small airways close
Closing capacity is the
absolute volume of gas in the lung when small airways close (CV +RV)
increases from 30% of TLC at age 20 to 55% by age 70
Closing volume is increased by
supine position, pregnancy, obesity, COPD, CHF, and aging
If CV> FRC airway closure occurs during
tidal breathing causing poorly ventilated or under-ventilated alveoli and intrapulmonary shunting
Oxygen in the blood is carried in two ways:
1-physical: dissolved in blood
2- chemical: bound to HGB (99.7% of O2)
Dissolved oxygen is not
clinically significant
Hemoglobin consists of:
4 protein subunits 2alpha and 2 beta chains
4 heme subunits
iron-porphyrin compound
Each hemoglobin molecule binds up to
4 oxygen molecules
each gram of HGB binds 1.34 mL of oxygen
The oxy-hemoglobin dissociation curve shows the
relationship between saturation of hemoglobin at a given plasma PO2
A right shift of the oxy hemoglobin curve is
right release at the tissues
lower affinity for O2
A left shift of the oxy hemoglobin curve is
left love- binds as much as it can because CO2 levels are lower
higher affinity
A left shift of the oxy hemoglobin curve can be caused by
decreased temperature, decreased CO2- hypocapnia, increased pH- alkalosis, decreased 2,3 diphosphoglycerate
A right shift of the oxyhemoglobin curve can be caused by
increased temperature, increased CO2- hypercapnia, decreased pH- acidosis, increased 2, 3 diphosphoglycerate
The haldane effect is when
oxygenation of blood displaces carbon dioxide from hemoglobin
- this occurs at the A/C membrane of the lungs
The Bohr effect is the
hemoglobin’s affinity for O2 is inversely related to CO2 levels
acidic environments cause a rightward shift- displaces O2 and allows CO2 to bind
At a PaO2 of 27, SaO2 is
50%
At a PaO2 of 40, SaO2 is
70%
At a PaO2 of 60, SaO2 is
90%
The DLCO tests the lungs
diffusing capacity for carbon monoxide (DLCO)
Normal DLCO is
> 75% of predicted, up to 140%
Mild DLCO is
60% to lower limit of normal
Moderate DLCO is
40-60%
Severe DLCO is
<40%
DLCO is indicated in the evaluation of
parenchymal and non-parenchymal lung diseases in conjunction with spirometry
CO2 can be transported in the blood via:
physical solution 5-10% (dissolved in blood)
chemically combined with amino acids of blood proteins 5-10% (bound to hemoglobin)
bicarbonate ions 80-90%- most CO2 is present in the blood as bicarb
The carbonic anhydrase equation is
CO2 + H2O –> Carbonic anhydrase–> HCO3- + H+
assists rapid inter-conversion of carbon dioxide and water into carbonic acid, protons, and bicarbonate ions
During the hamburger shift,
HCO2 leaves the RBCs and chloride enters to maintain electrical neutrality AKA “chloride shift”
Acid-base balance is maintained through
serum buffers, the lung and kidneys work together to maintain a normal acid-base balance
serum buffers work continuously
lungs- minutes
kidneys- days
Hypoxic hypoxia is a
issue within the lungs decrease of Fio2 (<0.21) alveolar hypoventilation V/Q mismatch R to L shunt supplemental O2 will help
Clinical examples of hypoxic hypoxia include
high altitudes, O2 equipment error, drug OD, COPD, pulmonary fibrosis, PE, atelectasis, congenital heart disease
Circulatory hypoxia is due to
reduced cardiac output
supplemental oxygen will have minimal effect
Clinical examples of circulatory hypoxia include
severe heart failure, dehydration, sepsis, SIRS
Hemic hypoxia is a
reduced hemoglobin content/function
supplemental O2 will have minimal effect
Clinical examples of hemic hypoxia include
anemias, carboxyhemoglobinemia
methemoglobinemia- nitrate poisoning or prilocaine
Demand/histotoxic hypoxia is due to
increased O2 consumption or inability to utilize O2
Supplemental O2 will help
Clinical examples of demand hypoxia include
fever, seizures, cyanide toxicity
Hypoxic pulmonary vasoconstriction is a
reflex contraction of pulmonary vasculature in response to a low regional partial pressure of oxygen
HPV is intended to
match regional perfusion to ventilation in the lungs
diverts blood away from hypoxic areas of the lungs to areas with better ventilation and oxygenation (aims to correct V/Q mismatch)
HPV is affected by
PAO2 levels, pH, PCO2, temperature
the mechanism of action of HPV is
alterations in leukotrienes and prostaglandin synthesis
inhibition of NO production
Increased PCO2 (acidosis) will lead to
vasoconstriction
Decreased PCO2 will lead to
vasodilation
In a hypoxic environment, it is important to note
pulmonary circulation vasoconstricts
HPV is reduced or eliminated by:
elevated fiO2 & volatile agents above 1 MAC
Causes of deadspace include
anything that causes decrease in pulmonary blood flow
pulmonary embolism, hypovolemia, cardiac arrest, shock
Causes of shunts include
anything that causes the alveoli to collapse or fill
mucus plugging, ET tube in right or left mainstem, atelectasis, pneumonia, pulmonary edema
Anatomical dead space is
air that is present in the airway that never reaches the alveoli and therefore never participates in gas exchange
Alveolar dead space is
air found within the alveoli that are unable to function, such as those affected by disease or abnormal blood flow
Physiologic dead space is equal to
anatomical dead space+ alveolar dead space
Deadspace can be calculated via
Bohr’s equation
deadspace= Vt (PaCO2-PeCo2)/PaCO2
PeCO2 is normally
2-5 mmHg less than PaCO2 due to mixing with anatomic dead-space during exhalation
increases with V/Q mismatch
An absolute shunt is
V/Q= 0
hypoxia unresponsive to supplemental oxygen
everything that isn’t an absolute shunt is considered a V/Q mismatch
Venous admixture is the reulut of
mixing of non-oxygenated blood with oxygenated blood distal to the alveoli
mixed venous oxygen tension represents the
overall balance between O2 consumption (VO2) and O2 delivery (DO2)
Factors that lower PVO2 include
decreased cardiac output
increased O2 consumption
decreased hemoglobin concentration
Shunt like alveoli (low V/Q) have
low PO2 and high PCO2
think venous blood
Deadspace-like alveoli have
high V/Q
high PO2 and low PCO2
think atmospheric air
Symptoms of upper respiratory infection include
elevated WBCs, mucopurulent nasal secretions, inflamed and reddened mucosa, positive chest findings (ex. congestion, rales), temperature above 37 degrees Celcius, tonsillitis, viral ulcer in oropharynx, fatigue, laryngitis, sore throat
Symptoms of allergy include
histamine mediated
sneezing, ash or boggy mucosa, itchy/runny nose, conjunctivitis, wheezing, hives, possible swollen lips, tongue, eyes or face, dry red and cracked skin
Fick’s law of diffusion is
rate of gas diffusion= diffusion coefficient x surface area of the membrane x (difference in partial pressure/ thickness of the membrane)
The alveolar gas equation states that
PAO2= (PB-PH2O) x Fio2- (PaCO2/0.8)
where PB= 760 mmHg
PH20= 47 mmHg
Arterial oxygen content can be calculated by
CaO2= (HB x 1.34 x SaO2) + (PaO2 x 0.003)
The alveolar-arterial oxygen tension gradient is
PAO2-PaO2
normal value is 5-15
Good indicator of overall gas exchange
The A-a gradient increases with
age, obesity, supine position, and heavy exercise
-age leads to increased closing capacity and a decrease in PaO2
Oxygen delivery can be calculated by
DO2= QT x CaO2 QT= cardiac output
Fick’s equation of oxygen consumption is
VO2= cardiac output x (CaO2-CvO2)
CO2/alveolar ventilation can be calculated by
PaCO2= total CO2 production/alveolar ventilation
shows that PACO2 levels are inversely proportionate to alveolar ventilation
The P/F ratio is found by
PaO2/FiO2
A normal P/F ratio is
400-500
A P/F ratio <300 indicates
mild ARDs
A P/F ratio <200 is consistent with
moderate ARDs
A P/F ratio <100 is consistent with
Severe ARDS
